Found this on Reddit:Required SimConnect API Reinstall, It's in the SDK\Core Utilities Kit\SimConnect SDK\LegacyInterfaces\FSX-XPACK folder.

So, that more or less confirms that it does NOT ship with SimConnect installed, but you can install it. That should just about do it in terms of an EXISTING PE installation being able to work with the Steam version.

If you don't have PE installed, though, I don't yet know if the installer will detect Steam FSX (it depends on what registry keys they use). I can add support for it once I found out what the keys are.

Got it working locally on a machine that didn't have FSX on it at all prior to that. The registry keys are the same, so the installer has no problem.

However, I had to do 3 things:1) install the FSX-SP1 SimConnect, located in: x:\steamapps\common\FSX\SDK\Core Utilities Kit\SimConnect SDK\LegacyInterfaces\FSX-SP1 2) remove Microsoft.FlightSimulator.SimConnect.dll from X:\steamapps\common\FSX\SDK\Core Utilities Kit\SimConnect SDK\lib\managed for FSX to run properly. YMMV.3) I had to configure PE to 'Run As Administrator' for the keyboard-based PTT to work

Evidently they have FSX running as Administrator, that's why the PTT had an issue initially. Now if you'll excuse me, I have to shower and burn these clothes.